In order to decrease the power loss of the torque converter and to improve the driveability and fuel comsumption of the automobile, a fluid operated clutch for directly coupling the impeller of the torque converter to the turbine under a predetermined driving condition is generally used.
Such a clutch for directly connecting the impeller with the turbine is so arranged that a clutch facing is pressed against a clutch disk by pressure oil introduced into a pressure oil chamber provided in the clutch. In a conventional clutch system, governor pressure which is produced by a governor valve in proportion to the speed of the vehicle is applied to the pressure oil chamber. The clutch system is so arranged that, when the governor pressure exceeds a predetermined level, the clutch facing is pressed against the clutch disk by the governor pressure. However, since the governor pressure is not sufficient to operate a conventional clutch, the clutch must be designed to be operated by the governor pressure. For example, the clutch facing is constructed by a plurality of plates or a pressure oil chamber having a great volume is provided. Therefore, the size of the clutch must be increased, which requires a large space for installing the clutch.
The present invention as its object provides a system which can remove the disadvantage in the conventional torque converter system.